U.S. patent number 9,485,690 [Application Number 14/116,821] was granted by the patent office on 2016-11-01 for system for connecting radio access nodes of a radio access network.
This patent grant is currently assigned to Telefonica, S.A.. The grantee listed for this patent is Luis Cucala Garcia, Francisco Javier Lorca Hernando, Primitivo Matas Sanz, Quiliano Perez Tarrero. Invention is credited to Luis Cucala Garcia, Francisco Javier Lorca Hernando, Primitivo Matas Sanz, Quiliano Perez Tarrero.
United States Patent |
9,485,690 |
Cucala Garcia , et
al. |
November 1, 2016 |
System for connecting radio access nodes of a radio access
network
Abstract
The system comprises a plurality of radio access nodes, or
cells, each of said cells providing a coverage area to a plurality
of user equipments, characterized in that each of said radio access
nodes is splitted into: a common processing section (1) which
performs a main processing stage; and a plurality of remote
transceiving sections (2a, 2b, 2c), each performing a local
processing stage complementing said main processing stage, being
operatively connected to said common processing section, and
constituting a sub-cell providing a coverage sub-area, wherein said
coverage area is distributed into said coverage sub-areas. The
method is arranged for carrying out said splitting of radio access
nodes.
Inventors: |
Cucala Garcia; Luis (Madrid,
ES), Matas Sanz; Primitivo (Madrid, ES),
Perez Tarrero; Quiliano (Madrid, ES), Lorca Hernando;
Francisco Javier (Madrid, ES) |
Applicant: |
Name |
City |
State |
Country |
Type |
Cucala Garcia; Luis
Matas Sanz; Primitivo
Perez Tarrero; Quiliano
Lorca Hernando; Francisco Javier |
Madrid
Madrid
Madrid
Madrid |
N/A
N/A
N/A
N/A |
ES
ES
ES
ES |
|
|
Assignee: |
Telefonica, S.A. (Madrid,
ES)
|
Family
ID: |
46085076 |
Appl.
No.: |
14/116,821 |
Filed: |
May 16, 2012 |
PCT
Filed: |
May 16, 2012 |
PCT No.: |
PCT/EP2012/059201 |
371(c)(1),(2),(4) Date: |
January 27, 2014 |
PCT
Pub. No.: |
WO2012/156482 |
PCT
Pub. Date: |
November 22, 2012 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140155075 A1 |
Jun 5, 2014 |
|
Foreign Application Priority Data
|
|
|
|
|
May 17, 2011 [ES] |
|
|
201130794 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
16/16 (20130101); H04W 28/26 (20130101); H04W
88/085 (20130101) |
Current International
Class: |
H04W
28/26 (20090101); H04W 16/16 (20090101); H04W
88/08 (20090101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Jonathan Gambini et al., "Radio over Telephone Lines in Femtocell
Systems", 21st Annual IEEE International Symposium on Personal,
Indoor and Mobile Radio Communications, Sep. 26, 2010, pp.
1544-1549. cited by applicant .
International Search Report of PCT/EP2012/059201 dated Aug. 16,
2012. cited by applicant.
|
Primary Examiner: Zewdu; Meless
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
The invention claimed is:
1. A system for connecting radio access nodes of a radio access
network, said radio access network comprising a plurality of radio
access nodes, or cells, each of said cells providing a coverage
area to a plurality of user equipments, each of said radio access
nodes is split into: a common processing section configured to
perform a main processing stage; and a plurality of remote
transceiving sections, each configured to perform a local
processing stage complementing said main processing stage, being
operatively connected to said common processing section, wherein
each remote transceiving section of said plurality of remote
transceiving sections is configured to provide radio coverage in a
sub-area of said coverage area, and constitutes a sub-cell of said
cell, wherein said coverage area is distributed into said coverage
sub-areas, wherein said common processing section is configured to
perform data processing functionalities between a radio resource
control layer and a modulation mapper of a physical layer, said
common processing section comprising the following processing
blocks in a communication direction between the common processing
section and the remote transceiving section: a code block
segmentation, a channel coding, a rate matching, a code block
concatenation, a circular buffer, a scrambling and a pre-modulation
mapper; wherein said pre-modulation mapper block is configured to
add the following information to a data stream: a type of
modulation to be applied in said remote transceiving section; and a
number of radio resources reserved to a user equipment; wherein
said radio resources are resources blocks, and said pre-modulation
mapper block is further configured to add an initial resource block
where data will be mapped at said remote transceiving section to
data stream, so that an output constitutes a lower data rate than
an output of a common complex-modulated modulator; and wherein said
plurality of remote transceiving sections include the following
blocks in the communication direction between the remote
transceiving section and the common processing section: a
quadrature (IQ) demodulation, a downconversion, an analog to
digital conversion, a cyclic prefix removal, a Fast Fourier
Transform (FFT) and Inverse Fast Fourier Transform (IFFT)
processing, a resource element demapper and a demodulation
demapper.
2. The system according to claim 1, wherein said common processing
section and said remote transceiving sections are connected by a
low bit rate communications network.
3. The system according to claim 1, wherein said radio access
network is a Long Term Evolution (LTE) or Universal Mobile
Telecommunication System (UMTS) radio access network.
4. The system according to claim 1, wherein said common processing
section is further configured to make use of as many data streams
as user equipments and devote every data stream to one of said
remote sections.
5. The system according to claim 1, wherein said radio access nodes
are femtonodes.
6. A method for connecting radio access nodes of a radio access
network, said radio access network comprising a plurality of radio
access nodes, or cells, each of said cells providing a coverage
area to a plurality of user equipments, the method comprising
splitting each of said radio access nodes into: a common processing
section configured to perform a main processing stage; and a
plurality of remote transceiving sections, each configured to
perform a local processing stage complementing said main processing
stage, wherein each remote transceiving section of said plurality
of remote transceiving sections is configured to provide radio
coverage in a sub-area of said coverage area, and constitutes a
sub-cell of said cell, wherein said coverage area is distributed
into said coverage sub-areas, wherein the method further comprises:
performing, by said common processing section, data processing
functionalities between a radio resource control layer and a
modulation mapper of a physical layer, said common processing
section comprising the following processing blocks in a
communication direction between the common processing section and
the remote transceiving section: a code block segmentation, a
channel coding, a rate matching, a code block concatenation, a
circular buffer, a scrambling and a pre-modulation mapper; adding,
by said pre-modulation mapper block, the following information to
data stream: a type of modulation to be applied in said remote
transceiving section; and a number of radio resources reserved to a
user equipment; further adding, by said pre-modulation mapper
block, an initial resource block where data will be mapped at said
remote transceiving section to data stream, so that an output
constitutes a lower data rate than an output of a common
complex-modulated modulator; and obtaining a lower data rate after
a downconversion process than an output of a common analog to
digital converted at an output of a demodulation demapper, said
demodulation demapper being one of the blocks included in the
communication direction between the remote transceiving section and
the common processing section of said plurality of remote
transceiving sections.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This is a National Stage of International Application No.
PCT/EP2012/059201 filed May 16, 2012, claiming priority based on
Spanish Patent Application No. P201130794 filed May 17, 2011, the
contents of all of which are incorporated herein by reference in
their entirety.
FIELD OF THE ART
The present invention generally relates, in a first aspect, to a
system for minimizing interferences between radio access nodes, or
cells, of a radio access network, and more particularly to a system
which comprises splitting said radio access nodes into a common
processing section and a plurality of remote transceiving
sections.
A second aspect of the invention relates to a method arranged for
carrying out said splitting of radio access nodes.
PRIOR STATE OF THE ART
Femtocells are small base stations that are installed at the
customer's or enterprise's premises in order to provide mobile
broadband coverage, like UMTS or LTE, in a limited area. The
femtonodes are connected to the mobile operator's core network by
means of a fixed broadband access network, like an ADSL line or a
fibre connection.
The current femtonode integrates all its functionalities within a
single enclosure, from the antennas which radiate the radio signals
to the Ethernet connection which supports the interface with the
mobile core network (Iuh in the case of UMTS, or S1 in the case of
LTE). This single-enclosure femtonode must provide the full
coverage of a home or an office area, and if its coverage is not
enough, its power must be increased or more femtonodes must be
installed.
There are also some other solutions for providing indoor coverage
in a distributed way. For example: Radio On Fibre (RoF) techniques.
In this case a single base station is installed in a building, and
the radio signals, before their transmission through the antennas,
are converted to an optical format and transmitted through a fibre
network along the building. At the other end of the fibre network,
some remote radio heads re-convert the signals to the radio format
and radiate them by means of antennas. Radio on coaxial cable
media. In this case a single base station is installed in a
building, and the radio signals are transmitted through a coaxial
cable network along the building up to some remote radio heads.
This remote radio heads can be fully passive, or they can include
some active elements. Some examples of coaxial cable solutions with
active elements are described in patents "WO2009149101A1 Remote
Distributed Antenna" and "U.S. Pat. No. 5,918,154A Communications
Systems Employing Antenna Diversity". Remote radio heads connected
to the base station by means of a digital interface. The main
representatives of this solution are the CPRI and the OBSAI
standards. In both cases the digital I/Q signals of the base
station, before they are converted to an analog format and
up-converted to radiofrequency, are digitally transmitted through a
fibre network. At the other end of the fibre network, some remote
radio heads convert the signals to analog and perform the final
frequency up-conversion, and radiate them by means of antennas.
Regarding the implementation of a femtonode, the 3GPP standard does
not specify any reference architecture for it. However, the
generation of both the downlink and the uplink physical signals
makes it necessary to implement a set of functional blocks.
In the downlink, the payload to be transmitted to the UE's goes
through the standard process in LTE; a code block segmentation,
channel coding, rate matching and code block concatenation. The
result is a set of Codewords, and every Codeword is a set of user
data before their formatting for radio transmission.
Once every Codeword has been generated, it goes through the
standard LTE scrambling process and the modulation mapper. The
function of the modulation mapper is mapping groups of bits to
complex modulated symbols according to a predefined modulation
scheme. The modulation scheme can be QPSK, 16-QAM or 64-QAM. In the
conventional architecture, the modulated segments are represented
by means of complex symbols, whose real and imaginary parts are
represented by means of digital words that range from 8 to 14 bits.
This is the same number of bits that are used in the DAC that is
placed after the IFFT block that is included in the OFDM signal
mapper.
In the standard LTE MU-MIMO architecture, the result of this
scrambling and modulation mapper process is fed to the Layer Mapper
block, whose function is to divide a Codeword between two or more
layers, up to four, and every layer is fed to an antenna. After the
layer mapping block, MIMO Precoding is performed.
The Resource Element Mapper is placed after the MIMO precoding
block, mapping the set of complex symbols to a set of subcarriers,
and the OFDM signal mapper performs the OFDM signal modulation by
means of an IFFT.
Finally, a Cyclic Prefix is added to the OFDM signal, a digital to
analog (DAC) conversion is performed, and the analog signal is
up-converted to radiofrequency before transmission.
In the Uplink, the receiving antenna detects the uplink signal from
the user terminal, which is down-converted, I/Q demodulated and
converted to a digital format by means of an Analog to Digital
Converter. The Cyclic Prefix Removal block removes the Cyclic
Prefix from the SC-FDMA signal, and the FFT and the IFFT blocks
perform the SC-FDMA demodulation. The Resource Element Demapper
extracts the modulated symbols from the set of assigned
subcarriers. The function of Demodulation Demapper block is the
opposite of the Modulation Mapper, i.e. to convert QPSK, 16-QAM or
64QAM symbols into a serial stream of binary digital words which is
fed to the descrambler and decoding units.
Problems with Existing Solutions
The main problem of the Radio On Fibre (RoF) or the Radio on
Coaxial cable techniques is that they are very costly and can only
be used in very big buildings which demand a high radio
capacity.
In the case of the Remote radio heads connected to the base station
by means of a digital interface, like CPRI or OBSAI standards, the
main problems of this solution are two: the data rate that must be
supported by the fibre network is high, with a minimum bit rate of
the order of 300 Mbps, and that it is very costly and can only be
used in very big buildings which demand a high radio capacity.
The main problem of the current femtonodes is the interference,
which can be produced between the femtonodes and the overlying
mobile broadband macro layer, or between the femtonodes themselves,
and a lot of effort is being devoted to address it [1], [2], [3],
[4].
The interference happens when the femtonodes and the macro layer
share the same frequency band, which is very common due to the
limited availability of bandwidth. There are some scenarios for the
interference problem:
1. When the femtonodes operate in the so called Closed Subscriber
Group mode (CSG) [5] [6]. In this case a User Equipment (UE), i.e.
a mobile phone, which is not included in the CSG list of a
femtonode will not be able to camp in it, and thus the UE will
perceive the femtonode signal as an interference that partially
blocks the wanted signal coming from the macrocell layer.
2. When the femtonodes do not operate in the Closed Subscriber
Group mode and thus any UE can camp in it, the coverage area of the
femtonodes can overlap between them, or can overlap the coverage
area of the macrocell layer. In the overlapping area, some physical
channels of the mobile broadband signal emitted by every femtonode
and which are always present, for example the Broadcast Channel,
will interfere between them.
3. When the femtonodes do not operate in the Closed Subscriber
Group mode and thus any UE can camp in it, the coverage area of the
femtonodes can overlap between them, or can overlap the coverage
area of the macrocell layer. In the overlapping area, the channels
that are dedicated for the user data communication from a wanted
femtonode can be simultaneously used by another unwanted femtonode.
In UMTS this means that a channelization code used by a femtonode
to communicate data to a UE equipment is also used by a neighboring
femtonode. In LTE this means that the UE will report the status of
the radio interface usage by means of a Channel Quality Indicator
(CQI), and that the radio resource assignment scheduler in its
serving femtonode will try to cope with the interference from an
unwanted femtonode but it will not always be possible to achieve
it.
These interference scenarios are always the result of two
fundamental limitations of the current femtonodes:
1. The femtonodes cannot communicate with each other or with the
macrocells, in order to coordinate its use of the radio
resource.
2. The femtonodes output power, which is enough to cover a home or
an office area, is high enough to provide a coverage area that
overlaps with that of the macrocells or with other femtonodes.
DESCRIPTION OF THE INVENTION
It is necessary to offer an alternative to the state of the art
which covers the gaps found therein, particularly related to the
lack of proposals which really allow avoiding interferences between
femtonodes or between femtonodes and the macrocell layer.
To that end, the present invention provides, in a first aspect, a
system for minimizing interferences between radio access nodes of a
radio access network, said radio access network comprising a
plurality of radio access nodes, or cells, each of said cells
providing a coverage area to a plurality of user equipments.
On contrary to the known proposals, the system of the invention, in
a characteristic manner it further comprises, in order to
distribute the coverage area of a single cell into many very small
cells, splitting said radio access nodes into: a common processing
section which performs a main processing stage; and a plurality of
remote transceiving sections, each performing a local processing
stage complementing said main processing stage, being operatively
connected to said common processing section, and constituting a
sub-cell providing a coverage sub-area, wherein said coverage area
is distributed into said coverage sub-areas.
Other embodiments of the method of the first aspect of the
invention are described according to appended claims, and in a
subsequent section related to the detailed description of several
embodiments.
A second aspect of the present invention comprises a method for
minimizing interferences between radio access nodes of a radio
access network, said radio access network comprising a plurality of
radio access nodes, or cells, each of said cells providing a
coverage area to a plurality of user equipments.
On contrary to the known proposals, the method of the invention, in
a characteristic manner, comprises splitting each of said radio
access nodes into: a common processing section for performing a
main processing stage; and a plurality of remote transceiving
sections, for performing each a local processing stage
complementing said main processing stage, wherein each of said
remote transceiving sections constitutes a sub-cell providing a
coverage sub-area, wherein said coverage area is distributed into
said coverage sub-areas.
Other embodiments of the second aspect of the invention are
described according to appended claims, and in a subsequent section
related to the detailed description of several embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
The previous and other advantages and features will be more fully
understood from the following detailed description of embodiments,
with reference to the attached drawings, which must be considered
in an illustrative and non-limiting manner, in which:
FIG. 1 shows the functional blocks for current standard LTE
downlink signal generation.
FIG. 2 shows the functional blocks for current standard LTE uplink
signal generation.
FIG. 3 shows, according to an embodiment of the system proposed in
the invention, a single processing section and multiple remote
sections for providing LTE coverage.
FIG. 4 shows, according to an embodiment of the system proposed in
the invention, the downlink distributed femtonode processing
section.
FIG. 5 shows, according to an embodiment of the system proposed in
the invention, the uplink distributed femtonode processing
section.
FIG. 6 shows, according to an embodiment of the system proposed in
the invention, the whole remote section.
FIG. 7 shows, according to an embodiment of the system proposed in
the invention, the processing section embedded within the ONT or
the ADSL router.
DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS
The goal of this invention is to distribute the coverage area of a
single femtonode into many very small cells, every one of them as
small as a single room. In this way the chances that the coverage
area of a femtonode overlaps with other femtonodes, or overlaps
with the macrocell layer, are greatly reduced. For this purpose the
femtonode is split into two sections, a Processing Section (1) and
a set of Remote Sections (2a, 2b, 2c), which are inter-connected by
means of a low bit rate communications network.
The Processing Section performs all the data processing
functionalities of a femtonode, from the Radio Resource Control
(RRC) layer to the Modulation Mapper of the Physical Layer (PHY),
including the support of the S1 and X2 interfaces in LTE, or the
Iuh interface in UMTS.
On the other hand, the Remote Section performs the Physical Layer
functionalities included between the Modulation Mapper and the
antenna, including from subcarrier modulation to radiofrequency
transmission and reception.
Both sections can be physically separated and interconnected by
means of some communications infrastructure, like an Ethernet LAN
or a Power Line Communications (PLC) network. This communications
infrastructure supports digital data as is the case of the present
proposal.
The split of the femtonode into two sections is done across the
Modulation Mapper in order to ensure that the bit rate to be
transmitted between the Processing Section and a Remote Section is
low enough, of the order of some tens of Mbps to be supported by an
Ethernet LAN or PLC network. This is possible thanks to the fact
that before the Modulation Mapper the data is fed by means of
Codewords, represented by discrete values that are not yet
converted to the full scale of the subsequent Digital to Analog
Converters (DAC).
Once the Modulation Mapping has been done in the Remote Section,
its output values, a block of complex-valued symbols, are then
represented by digital words with the same number of bits (from 8
to 14) than the DAC that will be used before the analog radio
section, which greatly increases the bit rate (from 8 to 14 times)
at the output of the Modulation Mapper, but this data stream
remains confined to within the Remote Section.
This low bit rate between the Processing Section and the Remote
Section is the main difference with respect to other
implementations that make use of some kind of remote radio units,
like CPRI [7] or OBSAI [8], which typically require bit rates in
excess of 300 Mbps that cannot be supported by many Ethernet LAN's
or PLC networks.
This invention makes it possible to connect many Remote Sections to
a single Processing Section, and every Remote Section can be placed
in a different location or room to provide LTE coverage around it,
as shown in FIG. 1. The output power of every Remote Section can be
adjusted individually and can be set to very low values, of the
order of -10 dBm, in order to provide coverage to a very limited
area and avoiding overlapping with the coverage from another Remote
Sections. The limited coverage of every Remote Section allows
reusing the radio spectrum in different Remote Sections, thus
applying the radio cellular concept to very small cells.
The architecture of the Processing Section and the Remote Section
are very similar to that of a standard HeNB. The Processing Section
updates the standard Multiple User MIMO (MU-MIMO) architecture,
making use of as many data streams or payloads as User Equipments,
devoting every data stream or payload to a single antenna and thus
to a single Remote Section. In the standard MU-MIMO architecture as
defined in 3GPP (as shown in FIG. 2) two Codewords are possible,
which are mapped to up to four antennas, in a one-to-many
configuration. In this invention the number of data streams or
payloads is not limited, as it is not the number of antennas
(equivalent to the number of Remote Sections), and there is a
one-to-one correspondence between one data stream or payload and a
single antenna or Remote Section (as shown in FIG. 3), and a Remote
Section can support more than one data stream or payload.
All through this invention description the femtonode concept can be
applied to an UMTS femtonode or HNB (Home Node B in 3GPP
terminology), or to an LTE/LTE-A femtonode or HeNB (Home eNode B in
3GPP terminology). However, the preferred embodiment of the
invention which will be described in this patent application will
be based in a HeNB.
Also all through this invention the concept of radio resource
refers in UMTS to a specific combination of scrambling code and
channelization code used in a given instant, and in LTE to a set of
OFDM subcarriers used in a given instant.
This invention splits the femtonode into two sections, a Processing
Section (1) and a set of Remote Sections (2a, 2b, 2c), which are
inter-connected by means of a local communications network, wired
or wireless, for example but not precluding any other
implementation, an Ethernet Local Area Network, a Power Line
Communications network or a wireless link.
This split is done in order to install low power transmitting
units, the Remote Sections, in those rooms which require UMTS or
LTE/LTE-A radio coverage, having every Remote Section devoted to
provide coverage to only that single room, and keeping most of the
processing functionalities of the femtonode in the Processing
Section.
The Processing Section performs all the data processing
functionalities of a femtonode, from the Radio Resource Control
(RRC) layer to just before the Modulation Mapper of the Physical
Layer (PHY), including the support of the S1 and X2 interfaces.
The Processing Section is basically a complete femtonode, from
which the following blocks have been removed: In the downlink
transmission chain (the transmission that goes from the femtonode
to the UE), all the functional blocks between the Modulation Mapper
and the transmitting antenna have been removed. In the uplink
reception chain (the transmission that goes from the UE to the
femtonode), all the functional blocks between the receiving antenna
and the Demodulation Demapper (conversion of symbols to bits) have
been removed.
The concepts of Modulation Mapper and Demodulation Demapper are
standard in LTE. The Modulation Mapper assigns groups of bits to
complex modulated symbols according to a modulation mode (e.g.
QPSK, 16QAM or 64QAM), and the Demodulation Demapper performs the
opposite function.
The downlink Processing Section makes use of as many data streams
or payloads as User Equipments, devoting every data stream or
payload to a single antenna and thus to a single Remote Section. In
this invention the number of data streams or payloads is not
limited, as it is not the number of antennas (equivalent to the
number of Remote Sections), and every data stream or payload is
directed to a single antenna or Remote Section, and more than one
data stream or payload can be directed to a Remote Section (as
shown in FIG. 4).
In the downlink part of the Processing Section, the payload to be
transmitted to the UE's goes through the standard process in LTE,
from code block segmentation, channel coding, rate matching and
code block concatenation. The result is a set of Codewords, and
every Codeword is a set of user data before their formatting for
radio transmission. In this invention every Codeword is devoted to
a single UE, and thus the MU-MIMO Layer Mapping and Precoding
functionalities are not necessary. Once every Codeword has been
generated, it goes through the standard LTE scrambling process.
In a conventional architecture, the scrambled Codeword would be fed
to the Modulation Mapper, whose function is to map groups of bits
to complex modulated symbols according to a predefined modulation
scheme. In this invention the Modulation Mapper is located in the
Remote Section. The output of the scrambler is fed to a
Pre-Modulation Mapper block, which adds some bits of information to
the output of the scrambler, that indicate: The type of modulation
that will have to be applied to the segment in the Modulation
Mapper at the Remote Section. The initial Resource Block where data
will be mapped in the Resource Element Mapper at the Remote
Section. The number of Resource Blocks which are reserved to the
intended User Equipment.
The output of the Pre-Modulation Mapper is then fed to the local
communications network to be transmitted to the Remote
Sections.
Additionally, other control information must also be sent to the
Remote Sections: the Physical Broadcast Channel (PBCH), the
Physical Downlink Control Channel (PDCCH), the Physical Multicast
Channel (PMCH), the Physical Control Format Indicator Channel
(PCFICH), and the Physical Hybrid Automatic Repeat Request
Indicator Channel (PHICH). These channels have a much lower bit
rate, and thus the total bit rate is mainly determined by the
payload.
The uplink subsection of the Processing Section receives the output
of the Demodulation Demapper of the Remote Section, after its
transmission through the local communications network. In LTE the
information bits shall correspond to PUSCH, PUCCH and PRACH
channels, being PUSCH the one with the highest bit rate and that
which mainly determines the total bit rate.
Every data from every Remote Section is descrambled and decoded,
and the output of every decoder is fed to the subsequent uplink
blocks of a standard femtonode, as shown in FIG. 5.
The Remote Section includes the remaining femtonode functionalities
that are not included in the Processing Section. The architecture
of the Remote Section was shown in FIG. 6.
In the Downlink, it includes all the functions between the
Modulation Mapper and the transmitting antenna, performing the
standard LTE OFDMA modulation. The Modulation Mapper receives the
output of the Pre-Modulation Mapper of the Processing Section,
after being transmitted through the local communications network.
The Modulation Mapper maps the data segments into OFDM subcarriers,
applies the modulation scheme (e.g. QPSK, 16 QAM, 64 QAM), and
represents the modulated segments by means of complex symbols,
whose real and imaginary parts are represented by means of digital
words that range from 8 to 14 bits.
The output of the Modulation Mapper is a parallel stream which is
fed to the Resource Element Mapper. The Resource Element Mapper
adds all the common channels that must be transmitted from the
Remote Section: the Primary Synchronization Channel (P-SCH), the
Secondary Synchronization Channel (S-SCH), the Physical Broadcast
Channel (PBCH), the Reference Signals (RS), the Physical Downlink
Control Channel (PDCCH), the Physical Control Format Indicator
Channel (PCFICH), and the Physical Hybrid ARQ Indicator Channel
(PHICH).
The output of the Resource Element Mapper is a parallel stream
which is fed to the IFFT block. The output of the IFFT block is a
stream of OFDM symbols, to which cyclic prefixes (CP) are added in
the CP Insertion block. The output of the CP Insertion block is fed
to a Digital to Analog Converter (DAC or D/A), whose output is a
baseband or intermediate frequency analog signal. This analog
signal is I/Q modulated, up-converted to the desired radiofrequency
and radiated through the transmitting antenna.
In the Uplink, the Remote Section includes all the standards
functions between the receiving antenna and the Demodulation
Demapper, performing the standard LTE SC-FDMA demodulation. For the
Remote Sections to successfully extract the data from the uplink
radio signal, additional information must be provided by the
Processing Section: The type of modulation in uplink. The initial
Resource Block where data will be mapped in uplink. The number of
Resource Blocks reserved for the user in uplink.
All this control information shall be provided by the Processing
Section through the local communications network.
The estimated bit rate between the Processing Section and a Remote
Section would be as a maximum the bit rate corresponding to a
64QAM-modulated coded stream and full use of radio resources (i.e.
all available channelization codes in UMTS, or 100 Resource Blocks
in LTE). Given that the bit rate associated with the other control
information is much lower (PDCCH, PBCH, PMCH, PHICH, and other
common channels), this gives a maximum of roughly 90 Mbps for LTE,
excluding other control information.
If radio resources are reused, it should be possible to assign the
whole set of radio resources to more than one user. In this case,
if N users are simultaneously assigned the same radio resources,
each with 100 Resource Blocks and 64QAM, the total bit rate would
be approximately 90.times.N Mbps.
In practice most scenarios will involve a much lower bit rate,
because not all the radio resources are in general reserved for a
single user.
Some embodiments of the invention are presented next:
One Processing Section and Many Remote Sections
This embodiment of the invention was shown in FIG. 1, where a
Processing Section is connected to many Remote Sections by means of
a local communications network. This embodiment of the invention is
intended to provide very small coverage areas, supported by the
Remote Sections, reducing the interference with the macrocell layer
and with other femtonodes, and reusing the same radio resources in
different Remote Sections.
Processing Section Integrated with Other Functionalities
This embodiment of the invention was shown in FIG. 7, where a
Distributed Femtonode Processing Section is embedded within another
equipment, typically but not precluding any other implementation,
within an ONT or an ADSL modem. In this way, it is possible to have
the Processing Section functionality and the ONT or modem
functionality integrated within a single box, and at the same
installing the Remote Section, or Remote Sections, in the most
suitable location to provide indoor coverage.
Remote Sections with No Radio Radio Resources Reuse
In this embodiment of the invention all the Remote Sections radiate
the same signal. In this way, the radio coverage of the femtonode
is uniformly distributed through the area to be covered, avoiding
coverage gaps and also avoiding areas of high radiated power which
can interfere with the macrocell layer operation.
As all the Remote Sections radiate the same signal, the User
Equipment mobility between different Remote Section coverage areas
is ensured, because no handover procedure is needed, because the
User Equipment does not perceive any difference between the signals
from different Remote Sections.
Remote Sections with Radio Resources Reuse
In this embodiment of the invention the Remote Sections can radiate
different signals. In this way, the radio coverage of the femtonode
is uniformly distributed through the area to be covered, avoiding
coverage gaps and also avoiding areas of high radiated power which
can interfere with the macrocell layer operation. On the other
hand, the radio resources (i.e. the occupation of a given piece of
spectrum at a given time) can be reused between different Remote
Sections, as far as there is no coverage gap between the Remote
Sections which make use of the same radio resource.
In the particular case of LTE, the Remote Sections will radiate a
set of two different radio channels:
1. Radio channels that are common to all the Remote Sections. These
are the Primary Synchronization Channel, the Secondary
Synchronization Channel, the Physical Broadcast Channel, the
Physical Multicast Channel, the Physical Control Format Indicator
Channel, and the Physical Hybrid Automatic Repeat Request Indicator
Channel. The Remote Sections radiate the same common channels with
no difference between them. However, the Cell Reference Signals in
each Remote Unit should comprise different sets of subcarriers,
according to the resources reserved for each of them; thus each UE
will be able to extract the relevant channel information without
interference from other Remote Units.
2. A radio channel that is specific to every Remote Section, the
Physical Downlink Shared Channel. This physical channel transports
the user data that is specific to every User Equipment. The LTE
standard divides the radio resource in so called Resource Blocks,
where every Resource Block comprises 12 subcarriers (180 KHz)
during one slot time (0.5 ms). In this embodiment of the invention,
an LTE Remote Section can use the same Resource Block that is being
used by another LTE Remote Section, provided that their coverage
areas do not overlap.
In order to reuse a Resource Block in different Remote Sections,
the Processing Section must know which Remote Section is providing
coverage to the User Equipment to deliver the needed Resource Block
to that Remote Section. For this purpose, and not precluding any
other possible implementation, the Processing Section can make use
of the following procedures: Forcing the User Equipment to send
periodic uplink Sounding Reference Signals, as defined in 3GPP TS
36.211 [9], in specific time and spectrum intervals. The Sounding
Reference Signals are detected by the Remote Section which is
serving the user Equipment and sent to the Processing Section.
Analyzing the uplink ACK/NACK messages from the User Equipment,
which are transported by means of the uplink Physical Uplink Common
Control Channel. The ACK/NACK messages [10] are detected by the
Remote Section which is serving the user Equipment and sent to the
Processing Section. Analyzing the uplink CQI (Channel Quality
Indicator) [11] messages from the User Equipment, which are
transported by means of the uplink Physical Uplink Common Control
Channel. The CQI messages are detected by the Remote Section which
is serving the user Equipment and sent to the Processing Section.
Analyzing the uplink Demodulation Reference Signals from the User
Equipment, which are transported by means of the uplink Physical
Uplink Common Control Channel and the Physical Uplink Shared
Channel. The Demodulation Reference Signals are detected by the
Remote Section which is serving the user Equipment and sent to the
Processing Section.
In order to ensure the mobility of a User Equipment between Remote
Sections, the Processing Section makes use of any of the procedures
that has been described to detect the actual location of the User
Equipment at any given instant. When the User Equipment moves from
the coverage area of one Remote Section to that of another Remote
Section, the Processing Section detects the Remote Section through
which the uplink information (e.g. Sounding Reference Signals,
ACK/NACK messages, CQI messages, Demodulation Reference Signals)
from the User Equipment is being received, and thus determines the
Remote Section that provides coverage to that User Equipment. Once
the Processing Section determines which Remote Section receives the
uplink data from the User Equipment, it will send in the downlink
to that Remote Section the resource blocks of the Physical Downlink
Shared Channel that are addressed to that specific User
Equipment.
The advantages of this invention are as follows:
The chances that the coverage area of the distributed femtonode
overlaps with that from other femtonodes are greatly reduced due to
the low power emitted from every Remote Section. This reduces the
overall level of interference detected by the femtonodes and by a
User Equipment, increasing the capacity of the radio network. The
chances that the coverage area of the distributed femtonode
overlaps with that from the macrocell layer are greatly reduced due
to the low power emitted from every Remote Section. This reduces
the overall level of interference detected by the femtonodes and by
a User Equipment, increasing the capacity of the radio network. In
particular, it reduces the level of interference detected by a User
Equipment which is served by the macro layer and not connected to a
nearby femtonode because not being authorized to be connected to
it. The radio resources can be re-used between different Remote
Sections, as their coverage areas do not overlap, which can improve
the capacity and the spectral efficiency of the femtonode. When
there is no User Equipment connected to a Remote Section, this
Remote Section can radiate only the common radio channels and not
the Physical Downlink Shared Channel, thus reducing the level of
interference. The interconnection between the Processing Section
and the Remote Sections can be supported by a low performance
Ethernet or PLC network, thanks to the requested low bit rate, as
opposed to other solutions like CPRI or OBSAI which require bit
rates in excess of 300 Mbps.
A person skilled in the art could introduce changes and
modifications in the embodiments described without departing from
the scope of the invention as it is defined in the attached
claims.
ACRONYMS
3GPP 3rd Generation Partnership Project
ACK/NACK Acknowledge/Not Acknowledge message
ADC Analog to Digital Converter
ADSL Asymmetric Digital Subscriber Line
CP Cyclic Prefix
CPRI Common Public Radio Interface
CQI Channel Quality Indicator
DAC Digital to Analog Converter
FFT Fast Fourier Transform
HNB Home Node B
HeNB Home evolved Node B
IFFT Inverse Fast Fourier Transform
LTE Long Term Evolution
LTE-A Long Term Evolution Advanced
OBSAI Open Base Station Architecture Interface
OFDM Orthogonal Frequency Division Multiplexing
OFDMA Orthogonal Frequency Division Multiple Access
ONT Optical Network Termination
PBCH Physical Broadcast Channel
PCFICH Physical Control Format Indicator Channel
PDCCH Physical Downlink Control Channel
PHICH Physical Hybrid ARQ Indicator Channel
PLC Power Line Communications
PRACH Physical Random Access Channel
P-SCH Primary Synchronization Channel
PUCCH Physical Uplink Control Channel
PUSCH Physical Uplink Shared Channel
QAM Quadrature Amplitude Modulation
QPSK Quadrature Phase Shift Keying
RS Reference Signals
SC-FDMA Single Carrier Frequency Division Multiple Access
S-SCH Secondary Synchronization Channel
UE User Equipment
UMTS Universal Mobile Telecommunication System
REFERENCES
[1] 3GPP TSG-RAN WG1 #62bis R1-105299, Considerations on Grouping
based Interference Mitigation among Co-located Femtocells [2] 3GPP
TSG-RAN WG1 #62bis R1-105693, Enabling communication in harsh
interference scenarios [3] 3GPP TSG-RAN WG1 #62bis, R1-105746, On
Macro-Femto interference handling [4] 3GPP TR 36.922 LTE TDD Home
eNodeB RF Requirements [5] 3GPP TR23.830 Architecture aspects of
Home NodeB and Home eNodeB [6] 3GPP TS 25.367 Mobility procedures
for Home Node B (HNB); Overall description; Stage 2 (Release 9) [7]
Common Public Radio Interface (CPRI); Interface Specification v4.2
[8] Open Base Station Architecture Initiative (OBSAI), BTS system
reference document Version 2.0 [9] TS 36.211 Evolved Universal
Terrestrial Radio Access (E-UTRA); Physical Channels and
Modulation. Section. 5.5.3 Sounding reference signal. [10] 3GPP TS
36.213, Evolved Universal Terrestrial Radio Access (E-UTRA);
Physical layer procedures. 8.3 UE ACK/NACK procedure [11] 3GPP TS
36.213, Evolved Universal Terrestrial Radio Access (E-UTRA);
Physical layer procedures. 7.2UE procedure for reporting channel
quality indication (CQI)
* * * * *